Automatic film advance mechanisms for still cameras are long known in the art, and typically employ some form of film propulsion means either integral with or connectable to the camera body and actuated in cooperation with the shutter release mechanism to advance in cooperation with the shutter release mechanism to advance the film automatically one frame after each exposure. Contemporary automatic film advance systems of this type are almost exclusively of the electric motor type. When the film supply is exhausted, the user must be appraised of the end of film condition either by suitable warning means, or alternatively by refusal of the film actuating mechanism to advance after a subsequent exposure. At this point the operator must make a deliberate reconfiguration of the camera by manual operation of some means to initiate rewind of the film. More recent developments in the camera art have simplified this to the state that merely a switch need be actuated by the operator to throw the film advance mechanism into a rewind configuration, whereupon the film is rewound into the cassette, and film rewind is automatically terminated. Such a manual actuation feature poses an inconvenience to the user, and typically necessitates incorporation of extra components into the camera to secure the requisite switching. Such switching typically involves either singly or in combination a change in mechanical linkage or actuation of an electrical switch directly. Accordingly, it is the object of this invention to provide an automatic rewind feature for an electrically-driven camera wherein the transition from film advancing mode to film rewinding mode is carried automatically without requiring a special manual operation by the operator. This operation should be carried out reliably, irrespective of film length, and therefore should require no special programming of the camera to return to the rewind configuration after a specified number of frames.
During the loading operation of conventional still cameras employing cassette type film dispensers it is generally necessary to thread the film to a takeup spool to provide adequate film engagement for film advance. Conventional cameras so threaded do not derive the principal propulsive power applied to the film from the take-up reel, but rather derive such power from an auxiliary drive sprocket integrally geared to the takeup reel, such that the drive sprocket supplied the motor power to the film, and the take-up spool is overdriven through a slip clutch so as to accept the film in a tight wrap during film advance. Thus, the film must be threaded at the beginning to insure proper disposition of film wrap about the take-up spool during the film advance operation. This threading process is typically time consuming, and frequently results in lost time to the user when he must change film rapidly, as for example in news coverage, sport coverage, and similar situations in which the photographer takes a great many pictures in rapid succession. Accordingly, it is the object of this invention to provide a film loading system wherein no such threading is necessary into the take-up spool and wherein the film may simply be loaded by inserting the cassette, pulling out an adequate amount of leader, and closing the film loading door.